 |
Previous Article | Next Article 
The Journal of Neuroscience, November 15, 1999, 19(22):10074-10081
Neural Representation of a Rhythm Depends on Its Interval
Ratio
Katsuyuki
Sakai1, 2,
Okihide
Hikosaka1,
Satoru
Miyauchi3,
Ryousuke
Takino4,
Tomoe
Tamada5,
Nobue Kobayashi
Iwata2, and
Mathew
Nielsen3
1 Department of Physiology, Juntendo University School
of Medicine, Tokyo 113-0033, Japan, 2 Department of
Neurology, Division of Neuroscience, Graduate School of Medicine,
University of Tokyo, Tokyo 113-0033, Japan,
3 Communications Research Laboratory, Kobe 651-24, Japan,
4 Shiraume Gakuen College, Tokyo 187-8570, Japan, and
5 Exploratory Research for Advanced Technology, Japan
Science and Technology Corporation, Kyoto 619-02, Japan
 |
ABSTRACT |
Rhythm is determined solely by the relationship between the time
intervals of a series of events. Psychological studies have proposed
two types of rhythm representation depending on the interval ratio of
the rhythm: metrical and nonmetrical representation for rhythms formed
with small integer ratios and noninteger ratios, respectively. We used
functional magnetic resonance imaging to test whether there are two
neural representations of rhythm depending on the interval ratio. The
subjects performed a short-term memory task for a seven-tone rhythm
sequence, which was formed with 1:2:4, 1:2:3, or 1:2.5:3.5 ratios. The
brain activities during the memory delay period were measured and
compared with those during the retention of a control tone sequence,
which had constant intertone intervals. The results showed two patterns
of brain activations; the left premotor and parietal areas and right
cerebellar anterior lobe were active for 1:2:4 and 1:2:3 rhythms,
whereas the right prefrontal, premotor, and parietal areas together
with the bilateral cerebellar posterior lobe were active for 1:2.5:3.5
rhythm. Analysis on individual subjects revealed that these activation
patterns depended on the ratio of the rhythms that were produced by the subjects rather than the ratio of the presented rhythms, suggesting that the observed activations reflected the internal representation of
rhythm. These results suggested that there are two neural
representations for rhythm depending on the interval ratio, which
correspond to metrical and nonmetrical representations.
Key words:
rhythm; short-term memory; metrical representation; nonmetrical representation; interval ratio; cerebellar anterior lobe; cerebellar posterior lobe; right hemisphere; left hemisphere
 |
INTRODUCTION |
Rhythm is a flow of time, a series
of time intervals marked off by the onsets of sensory or motor events,
such as tones, flashes of lights, and steps in dances. Thus, rhythm is
a supramodal entity that is determined solely by time information. The
fact that we can recognize, discriminate, and reproduce a large number
of rhythms suggests that individual rhythms can be internally
represented, but its neural mechanism has not been well understood.
To date, most of the studies on neural processing of rhythm have been
based on brain-damaged patients. Rhythm processing can be selectively
impaired without any deficit in melody processing, suggesting the
presence of a neural system specialized for rhythm (Peretz and
Kolinsky, 1993 ). A number of studies have shown that the left cerebral
hemisphere is involved in rhythm processing (Gordon and Bogen, 1974 ;
Robinson and Solomon, 1974 ; Brust, 1980 ; Mavlov, 1980 ; Polk and
Kertesz, 1993 ), but others indicated that the processing of rhythm is
not clearly lateralized (Peretz and Morais, 1980 ; Peretz, 1990 ). The
variation in the location and size of the lesions hampered the precise
localization of the responsible neural structures.
The inconsistency among these studies may be attributable to the
fact that they used actual music as a test stimulus, which contains
various types of rhythms. In this respect, previous psychological studies have identified an important constraint. Essens (1986) has
shown that rhythms formed with ratios expressed as small integer values
(1:2, 1:3, or 1:4) can be reproduced precisely, whereas rhythms related
with larger values (1:5) or noninteger values (1:2.5 or 1:3.5) may be
represented inaccurately. Based on the finding, Essens and Povel (1985)
have proposed two modes of rhythm representation: metrical and
nonmetrical representations. Metrical representation is to map a rhythm
onto a temporal reference frame called an internal clock, by which the
series of time intervals are metrically related with one another.
Rhythms formed with small integer ratios belong to this class. However,
this strategy cannot be applied to the rhythms formed with large ratios
or noninteger ratios. These rhythms are represented in a nonmetrical
manner with which the series of time intervals are maintained as
independent, unrelated values. This theory predicts that the neural
correlates for rhythm processing may be composed of separate neural
networks depending on the interval ratio of the rhythm.
In the present study, we have used functional magnetic resonance
imaging (fMRI) to identify the neural representation of rhythm and
tested whether there are two types of neural representation of rhythm,
which correspond to metrical and nonmetrical representations. For this
purpose, we used rhythms with their time intervals formed with 1:2:4,
1:2:3, and 1:2.5:3.5 ratios. We took advantage of fMRI to make
selective measurement of brain activations during the memory delay
period, which would reflect the neural activation underlying the
internal representation of rhythm.
 |
MATERIALS AND METHODS |
Subjects
Six normal subjects participated in the study (four males and
two females; age 27-44; all right-handed). None of them were professional musicians. Informed consents were obtained from all the
subjects before the study. The experimental protocol was approved by
the ethics committee of the Communications Research Laboratory (Kobe, Japan).
Behavioral paradigm
A sequence of seven short tone bursts was presented to the
subjects. Each tone had the same frequency: 1 kHz; rise-fall time, 5 msec; plateau, 20 msec; and intensity, 95 dB. The six intervals marked
off by the onsets of the seven tones were determined to comprise two
short (S), two intermediate (I), and two long intervals (L), where the
S, I, and L were related with 1:2:4 (1:2:4 rhythm), 1:2:3 (1:2:3
rhythm), or 1:2.5:3.5 (1:2.5:3.5 rhythm) ratios (Fig. 1). By taking all the possible orders of
the two Ss, Is, and Ls (e.g., SISLLI), we created 90 (6C2 × 4C2 × 2C2) sequences for each of
the three types of the rhythm sequence. The duration of the rhythm
sequence, as measured by the time interval from the onset of the first
tone to the onset of the last tone, was randomly chosen from 3220, 3360, 3500, 3640, and 3780 msec.

View larger version (25K):
[in this window]
[in a new window]
|
Figure 1.
Task procedure. Procedure of a task to examine the
short-term memory of rhythm. An experiment consisted of 120 trials. For
each trial, the subjects were presented with a sequence of seven tones
during the first 4.0 sec and were asked to keep it in memory for 10.8 sec. At the last 1.8 sec of the memory delay period, the scans were
performed. During the subsequent 5.2 sec period, the subjects
reproduced the maintained sequence by pressing a button. The intertone
time intervals of the tone sequence was related with 1:2:4 ratio (1:2:4
rhythm), 1:2:3 ratio (1:2:3 rhythm), or 1:2.5:3.5 ratio (1: 2.5: 3.5 rhythm), and the total duration of the sequence was varied across
trials ranging from 3220 to 3780 msec. The control sequence consisted
of seven tones separated by a fixed intertone
interval.
|
|
The subjects were asked to hold the presented rhythm sequence in memory
for a period of 10.8 sec and then to reproduce it by pressing a button
with the right index finger. Instruction was given to keep the relative
relations of the time intervals, as well as the absolute time intervals
of the presented sequence.
The memory performance was assessed based on the reproduced sequence of
button presses. Three measures were used for this purpose: order of the
time intervals classified as S, I, and L; ratio of the S, I, and L; and
duration of the sequence.
Order. The six time intervals of button pressing in the
reproduced sequence were classified into two Ss, two Is, and two Ls. The order of the three classes of the time intervals (e.g., SISLLI) was
compared with that of the presented tone sequence. If the order was
different, the trial was regarded as an error and was eliminated from
the following behavioral data analysis.
Ratio. Subsequently, we calculated the ratios of the button
press intervals of the reproduced sequence. The mean of the two Is and
the mean of the two Ls of reproduced rhythm was respectively divided by
the mean of the two Ss. The ideal ratios would be 2 and 4 for 1:2:4
rhythm, 2 and 3 for 1:2:3 rhythm, and 2.5 and 3.5 for 1:2.5:3.5 rhythm.
Duration. Another index for the accuracy of retention was
the duration of the sequence. The regression analysis was performed on
the duration of the reproduced sequence with that of the presented tone
sequence. Ideally, these durations should be correlated linearly with a
slope of 1.0 and an intercept of 0.
In the present study, we were interested in the rhythm, which can be
expressed by the order and ratio. To eliminate the effects of
the processes required for retention of absolute time intervals (duration), we also presented the control tone sequences (control), which were formed with seven tones separated by a constant interval. The total duration of the control sequence was randomly chosen from
3220, 3360, 3500, 3640, and 3780 msec to match that of the rhythm
sequences. The comparison between the rhythm sequence (order + ratio + duration) and control sequence
(duration) would selectively reveal the processes for retention of the
rhythm (order + ratio).
fMRI data acquisition
Before the fMRI experiments, the subjects underwent practice
sessions using 10 of the 90 sequences for each type of the rhythm sequence. For fMRI experiments, the rhythm sequences were chosen from
the remaining 80 sequences. Each sequence was used only once in each experiment.
An experiment comprised 120 trials, each of which is composed of the
tone presentation period (4 sec), memory delay period (10.8 sec),
followed by the reproduction period (5.2 sec) (Fig. 1). The subjects
fixated their gaze at the center spot on the screen and were not
allowed to move any body parts or to vocalize the rhythms throughout
the experiment, except for button presses during the reproduction
period. The motion of the subject's head was minimized by using a
strap around the forehead, bite bar, and ear fixation blocks. In the
tone presentation period, the tone sequence was delivered to a
headphone through a pair of plastic tubes (length, 180 cm), and the
subjects kept the sequence in memory during the memory delay period. At
the end of the delay period, a brief high-pitched tone (frequency, 2 kHz; duration, 30 msec) was presented, which served as a cue to
reproduce the presented tone sequence with button presses. The subjects
had to reproduce the sequence within the 5.2 sec reproduction period, after which the next trial started.
For measurement of brain activation, we used Siemens (Erlagen, Germany)
Vision 1.5 tesla scanner equipped with a circular polarized head coil.
Fourteen slices of T2*-weighted gradient-echo echo-planar images
[repetition time (TR), 20 sec; echo time (TE), 66 msec; inversion time
(TI), 300 msec; flip angle (FA), 90 degree] were collected within the
1.8 sec period at the end of the TR with the use of clustered volume
acquisition (Edmister et al., 1999 ; Talavage et al., 1999 ). The images
of 7 mm thickness [field of view (FOV), 220 × 220 mm; matrix,
128 × 128] were obtained parallel to the line connecting the
anterior and posterior commissure (AC-PC line). The AC-PC line was
determined based on the structure images obtained before the functional
experiments (Turbo FLASH; TR, 2.8 sec; TE, 4 msec; TI, 300 msec; FA, 15 degree; matrix: 256 × 256; FOV, 256 × 256 mm; slice
thickness, 1 mm). The timing of the scans was adjusted to start 9 sec
after the end of the tone presentation period. Therefore, even if we
take into account the delay of hemodynamic response, the
auditory-related activity should have almost returned to the baseline
level at the time of scans (Kwong et al., 1992 ; Buckner et al., 1996 ).
Indeed, our supplementary experiments conducted by using 2.5 sec
interscan interval (using TR of 2.5 sec) have shown that no significant activation relative to rest was present in the primary auditory area
7.5 sec after the cessation of the auditory stimuli (our unpublished
observation). In the present study, a series of the volume of
brain images was acquired with long interscan intervals (20 sec). This
sparse temporal sampling procedure (Hall et al., 1999 ) was advantageous
in that the scan noise did not hamper the perceptual and encoding
processes for the presented rhythm. In addition, no movements occurred
during the period for at least 13.0 sec before the time of the scans.
Therefore, the magnetic resonance signals obtained would reflect the
brain activations specifically associated with the retention of rhythms.
The following two sets of functional MRI experiments were performed,
with their orders counterbalanced across the six subjects.
Experiment 1. The experiment comprised 120 task trials: 40 trials of 1:2:4 rhythm, 40 trials of 1:2:3 rhythm, and 40 trials of
control. Ten trials for each type of the sequence were performed successively in a block. The blocks for the three types of the sequence
were alternated in a counterbalanced order and were repeated for four
times (e.g., 1:2:4 rhythm × 10 trials 1:2:3 rhythm × 10 trials control × 10 trials 1:2:3 rhythm × 10 trials
1:2:4 rhythm × 10 trials control × 10 trials
...). After two dummy scans, the task procedure was
started while a series of 120 scans separated by a 20 sec interscan
interval were performed for the 120 trials.
Experiment 2. Experiment 2 was conducted using the same
experimental procedure as experiment 1, except that 1:2.5:3.5 rhythm was used instead of 1:2:3 rhythm.
fMRI data analysis
Location of active areas. First, we performed a
statistical parametric analysis on the functional images of the six
subjects to identify the brain areas associated with retention of
rhythms. For each experiment, the 120 functional images were realigned to the first image of each subject and were stereotaxically normalized into the T2 template of the standard brain using the software of SPM96
(Welcome Department of Cognitive Neurology, London, UK, http://www.fil.ion.ucl.ac.uk) (Friston et al., 1995 ). The images were
then smoothed with a gaussian filter of 4.5 mm full-width half-maximum
(FWHM). After application of temporal high-pass filter (400 sec) to the
time course of magnetic resonance signals, the confounding effect of
variation in the global magnetic resonance signal intensity across the
subjects was removed by ANCOVA. Subsequently, the time series of
magnetic resonance signals was cross-correlated with a boxcar reference
function derived from the alternation of the task blocks. The reference
function was not shifted because of the usage of long TR (20 sec). For
experiment 1, 1:2:4 and 1:2:3 rhythms were respectively compared with
control. For experiment 2, 1:2:4 and 1:2.5:3.5 rhythms were
respectively compared with control. A statistical parametric map of the
t statistics was constituted from the resulting voxel values
and was transformed to the unit normal distribution (SPM{Z},
thresholded at 3.09). Taking the spatial extent of activation into
consideration, a corrected p value of 0.05 was then used as
a final threshold for significance.
Correlation of activation with memory performance. The above
statistical parametric analysis provides the averaged brain activations for the six subjects. However, as will be shown in the behavioral data
in Results, the memory performance differed across the subjects. Therefore, we also analyzed the brain activation pattern for each subject and correlated it with the memory performance. Instead of
normalizing the anatomical structures into the Talairach space (Talairach and Tournoux, 1988 ), the foci of significantly increased activation was mapped onto the anatomical echo-planar images for each
subject. After application of a gaussian filter with FWHM of 4.5 mm,
the brain areas with significantly increased activities for rhythm
compared with control were identified using a cross-correlation method
(thresholded at cross-correlation coefficient of 0.35).
 |
RESULTS |
Behavioral data
The memory performance was assessed based on the order, ratio, and
duration of the reproduced rhythms (examples shown in Fig. 2a). None of the six subjects
showed error rates above 10%. The error rates were not significantly
different between 1:2:3 and 1:2:4 rhythms (experiment 1, t(1,5) = 2.0; p > 0.1) but were significantly larger for 1:2.5:3.5 rhythm than 1:2:4
rhythm (experiment 2, t(1,5) = 2.91;
p < 0.05). In Figure 2b are shown the
reproduced ratios for the three types of rhythms, respectively, for the
six subjects. The mean ratio for the six subjects was 1:2.06:4.04 and 1:2.02:3.18, respectively, for 1:2:4 and 1:2:3 rhythms in experiment 1, and 1:2.01:4.00 and 1:2.33:3.69, respectively, for 1:2:4
and 1:2.5:3.5 rhythms in experiment 2. For 1:2.5:3.5 rhythm, the
reproduced ratio for 2.5 was significantly smaller than 2.5 (t(1,5) = 3.40; p < 0.05), and that for 3.5 was significantly larger than 3.5 (t(1,5) = 2.84; p < 0.05). In contrast, the reproduced ratios for 1:2:4 and 1:2:3 rhythms
were not significantly different from the original ratios except for
that for 3 in 1:2:3 rhythm, which was larger than 3 (t(1,5) = 6.76; p < 0.05) [for further analysis, see below (Correlation of activation with
memory performance)]. The duration of the sequence was maintained
fairly precisely for all the rhythms; all the six subjects showed
significant linear correlation
(r2 > 0.5) between the total
duration of the reproduced sequence and that of the presented sequence.
For all the subjects and tone sequences, the slopes and intercepts of
the regression lines were close to 1.0 and 0, respectively (Fig.
2b).

View larger version (31K):
[in this window]
[in a new window]
|
Figure 2.
Behavioral data. a, Three examples
of the presented tone sequence (circles with lines) and
the reproduced sequence (crosses) obtained from one
subject are shown for 1:2:4, 1:2:3, and 1:2.5:3.5 rhythms and control.
b, Summary of the behavioral data from six subjects.
Left, Reproduced ratios shown respectively for the six
subjects. Each X represents the mean value for one
subject. Middle, Right, Means of the
slopes (middle) and intercepts (right) of
the regression lines between the total duration of reproduced and
presented sequences. Error bars indicate the SEs. Data from experiment
1 (top) and experiment 2 (bottom).
|
|
fMRI data
Location of active areas
Comparisons of 1:2:4, 1:2:3, and 1:2.5:3.5 rhythms with control
revealed brain areas associated with retention of the rhythm components
(Table 1). 1:2:4 rhythm was tested twice
(experiments 1 and 2), and activations in the left premotor and
parietal areas were consistently observed, confirming the
reproducibility of the finding (Fig.
3a). In addition, almost the
same set of brain areas was active for 1:2:3 rhythm. In contrast, the
activation pattern for 1:2.5:3.5 rhythm was completely different; the
right prefrontal, premotor, and parietal areas were active. The
anterior part of the right prefrontal cortex was active only for
1:2.5:3.5 rhythm but not for 1:2:4 and 1:2:3 rhythms (Fig.
3b). The analysis of individual subjects showed that
this prefrontal activation focus was located within the anterior
part of the middle frontal gyrus close to the inferior frontal gyrus
(Fig. 4b, blue
circle). Additional activation foci were found in the cerebellum;
the right anterior lobe was active for 1:2:4 and 1:2:3 rhythms but not
for 1:2.5:3.5 rhythm, whereas the bilateral cerebellar posterior lobe was active for 1:2.5:3.5 rhythm but not for 1:2:4 rhythm (Fig. 3b). Only the right posterior lobe was active for 1:2:3
rhythm. Individual subject analysis showed that the activation foci in the cerebellar anterior lobe were located in the quadrangular lobule
[corresponding to hemispheric lobule IV (HIV)-HV] (Fig. 4a, pink circle), whereas the foci in the
posterior lobe were located within the simplex lobule and the
superior semilunar lobule of the cerebellum (corresponding to HVI-crus
I of HVIIa) (Fig. 4b, green circle).

View larger version (74K):
[in this window]
[in a new window]
|
Figure 3.
Statistical parametric analysis. a,
Statistical parametric maps (SPM{z}) of the six subjects when
1:2:4, 1:2:3, and 1:2.5:3.5 rhythms were respectively compared with
control. The foci of significantly increased activities were rendered
onto the surface template of the standard brain as implemented in SPM96
(Welcome Department of Cognitive Neurology, London, UK) and are shown
in red. b, Activation foci in
a are shown in three slices at 18 mm above
(left), 16 mm below (middle), and 22 mm
below (right) the level of the AC-PC line; the
prefrontal cortex (blue circle), cerebellar anterior
lobe (pink circle), and cerebellar posterior lobe
(green circle). White dotted lines
in the cerebellum indicate the primary fissure that separates the
anterior and posterior lobes of the cerebellum. The
right corresponds to the right hemisphere.
|
|

View larger version (53K):
[in this window]
[in a new window]
|
Figure 4.
Individual subject analysis. The distribution of
the interval ratios of the reproduced rhythms, shown as histograms and
rasters. Data are shown for 40 trials of 1:2:4
(a) and 1:2.5:3.5 (b)
rhythms in experiment 2. Abscissa of the histogram and raster
represents the reproduced ratio. The smaller ratios are shown in
blue, and larger ratios are shown in red.
For the raster display, trials have been sorted such that the smaller
ratios are arranged in the decrementing order from top
to bottom. The ratios for the presented rhythms are
indicated by the two vertical dotted lines. The
activation maps for each subject are shown in three slices in which
significant activations are shown in orange. The
right corresponds to the right hemisphere. White
dotted lines in the cerebellum indicate the primary fissure.
a, Activation pattern for 1:2:4 rhythm. The left
premotor cortex (yellow circle) and the right
cerebellar anterior lobe (pink circle) were
consistently active, except for subject 2. b, Activation
pattern for 1:2.5:3.5 rhythm. Note the difference in the ratio
distribution and activation patterns across the subjects. For the
premotor cortex (yellow circle), the right side
was active in subjects 1-4, whereas the left side was active in
subjects 5 and 6. The prefrontal cortex (blue circle)
was active in subjects 1-5, most prominently in subjects 1 and 2. The
cerebellar posterior lobe (green circle) was
bilaterally active in subjects 1-3, whereas the right cerebellar
anterior lobe (pink circle) was active in
subjects 4-6.
|
|
Correlation of activation with memory performance
As shown in Figure 2b, the memory performance
for 1:2:4 and 1:2:3 rhythms was not different across the six subjects,
whereas that for 1:2.5:3.5 rhythm considerably differed with respect to its reproduced ratios. The reproduced ratio for 2.5 ranged from 2.15 to
2.45, and that for 3.5 ranged from 3.52 to 3.92 among the six subjects.
To further analyze the performance of each subject, we plotted the
reproduced ratios for the 40 trials for 1:2:4 and 1:2.5:3.5 rhythms
(experiment 2) in histograms and rasters (Fig. 4). Histograms for 1:2:4
rhythm revealed two peaks of the reproduced ratios at 2 and 4 for all
the six subjects (Fig. 4a). On the other hand, for 1:2.5:3.5
rhythm, the peaks were found at 2.5 and 3.5 for subjects 1-3, whereas
additional two peaks were found at 2 and 4 for subjects 4-6 (Fig.
4b). For subject 6, the peaks at 2 and 4 were higher than
those at 2.5 and 3.5. The results indicated that the increased variance
in the reproduced ratios and deviation of them from the original ratios
for 1:2.5:3.5 rhythm were because of these additional peaks.
Furthermore, rasters in the figure have shown that the subjects
reproduced the rhythms in either 1:2.5:3.5 or in 1:2:4 ratios. Whenever
the subject reproduced the 1:2.5 ratio as 1: 2, he reproduced the 1:3.5
ratio as 1:4 in the same trial. The proportion of the two types of
reproduction, 1:2.5:3.5 or 1:2:4 ratios, in the 40 trials was
varied across the subjects.
Looking into the activation maps of each subject for 1:2:4 rhythm, the
active areas were found in the left premotor cortex and the right
cerebellar anterior lobe but not in the prefrontal cortex, consistent
across the six subjects (Fig. 4a). In contrast, for
1:2.5:3.5 rhythm, subjects 1-3 showed prominent activation in the
right prefrontal cortex, right premotor cortex, and the bilateral
cerebellar posterior lobe (Fig. 4b), whereas subjects 5 and
6 showed activation in the left premotor cortex and the right
cerebellar anterior lobe. Thus, the brain activation patterns of
subjects 5 and 6, who reproduced the 1:2.5:3.5 rhythm in 1:2:4 ratio,
were quite similar to those when 1:2:4 rhythm was presented (Fig.
4a). This finding suggests that the brain activation pattern depends on the ratios of the reproduced rhythms rather than the ratio
of the presented rhythms.
 |
DISCUSSION |
Two modes of neural representation for rhythm
Earlier psychological studies have, based solely on the behavioral
data, proposed two types of rhythm representation depending on the
interval ratio of the rhythm (Essens, 1986 ). The aim of the present
study was to test whether these metrical and nonmetrical representations recruit different sets of neural network. To elucidate the internal representation of rhythm, we used a short-term memory task
in which the subjects maintained a rhythm internally during the delay
period. However, MRI scans themselves produce rhythmic noise and would
have severely disturbed the experiment if they had been performed
during the tone presentation period or memory delay period. To
eliminate the interactive effects of the scan noise on the perceptual
and memory processes, we used a sparse temporal sampling procedure
(Hall et al., 1999 ) with clustered volume acquisition (Edmister et al.,
1999 ; Talavage et al., 1999 ) so that no scan was performed during the
delay period. The dependence of brain activation patterns on the
reproduced rhythm rather than the presented rhythm (as shown in Fig.
4b) strongly suggests that the measured brain activations
reflect the internal representation of rhythm.
The present study used three types of rhythm whose interval ratios were
expressed as 1:2:4, 1:2:3, and 1:2.5:3.5, respectively. According to
the theory proposed in the psychological literature (Povel,
1984 ; Essens and Povel, 1985 ; Povel and Essens, 1985 ), the
former two rhythms are represented in a metrical form, whereas the
latter one is represented in a nonmetrical form. The behavioral data in
the present study were consistent with this idea; the reproduction of
1:2:4 and 1:2:3 rhythms was precise, whereas that of 1:2.5:3.5 rhythm
was inaccurate, especially in its reproduced ratio. Interestingly, some
subjects unintentionally transformed the 1:2.5:3.5 rhythm into 1:2:4
rhythm, which was consistent with the finding of Essens (1986) . It has
also been shown that voluntary motor behaviors tended to fall into a
time sequence related with 1:2 ratios (Essens and Povel, 1985 ; Fulop et
al., 1992 ). Together, the results suggest that a rhythm is represented,
by default, in a metrical form rather than a nonmetrical form.
Our functional imaging data indicated that the brain activation
patterns for 1:2:4 and 1:2:3 rhythms were quite similar but were
completely different from that for 1:2.5:3.5 rhythm. First, the right
prefrontal cortex was active for 1:2.5:3.5 rhythm but not for 1:2:4 and
1:2:3 rhythms. Second, the cerebellar posterior lobe was bilaterally
active for 1:2.5:3.5 rhythm, whereas the right cerebellar anterior lobe
was active for 1:2:4 and 1:2:3 rhythms. Third, the right hemisphere was
predominantly active for 1:2.5:3.5 rhythm, whereas the left side was
more active for 1:2:4 and 1:2:3 rhythms. Considering that retention of
1:2.5:3.5 rhythm was more difficult than 1:2:4 and 1:2:3 rhythms (as
shown in the increase in the error rate), the difference in the brain activation pattern could reflect the level of attention required for
the memory task. We think that this is unlikely, however, because
different sets of brain areas were activated in these conditions, some
areas showing clear double dissociation. Instead, the results suggest
the presence of two distinctive neural representations of rhythm.
Prefrontal cortex
The prefrontal cortex has been regarded as the key structure for
working memory, and its activity was shown to reflect the on-line
processing of memorized materials (Funahashi et al., 1989 ; Goldman-Rakic, 1996 ; Cohen et al., 1997 ; Courtney et al., 1997 , 1998 ).
Involvement of the prefrontal cortex in memory of temporal information
has been shown in animal study (Niki and Watanabe, 1979 ). The present
study has shown that the right side of the prefrontal cortex located in
the anterior part of the middle frontal gyrus was active only for
1:2.5:3.5 rhythm. Its stereotaxic coordinates (42, 46, 18) were close
to the areas activated in retention of melody and pitch (Zatorre et
al., 1992 , 1994 ). Because we used isopitch tone sequence, the
prefrontal activity may be related generally to the manipulation or
monitoring of memorized information (Petrides, 1994 ; Fletcher et al.,
1998 ; Mangels et al., 1998 ).
In contrast, the absence of the prefrontal activation for 1:2:4 and
1:2:3 rhythms may suggest that metrical representation does not require
additional monitoring processes relative to the control sequence. In
metrical representation, the maintenance of a single time interval
alone allows to specify all the other time intervals of a rhythm.
Cerebellum
We found a clear double dissociation between the cerebellar
anterior and posterior lobe activations, the former being active for
1:2:4 rhythm, and the latter being active for 1:2.5:3.5 rhythm. The
anterior lobe of the cerebellum, especially HIV-HV, is related to the
ipsilateral upper limb movements (Nitschke et al., 1996 ; Allen et al.,
1997 ), whereas the posterior lobe, especially HVI-HVIIa, may be
involved in higher order cognitive processes, such as attention and
working memory (Allen et al., 1997 ; Desmond et al., 1997 ). From this
perspective, the right anterior lobe activation for 1:2:4 and 1:2:3
rhythms might reflect the preparatory processes for the following
reproduction with the right index finger. This seems unlikely,
however, because the primary motor cortex or supplementary motor area,
which has been shown to be active in motor imagery or motor
preparation (Roland et al., 1980 ; Stephan et al., 1995 ; Porro et al.,
1996 ), was not active in the present study.
In contrast, the cerebellar posterior lobe has been shown to be related
to explicit temporal representation (Ivry et al., 1988 ; Ivry, 1993 ;
Jueptner et al., 1996 ; Mangels et al., 1998 ; Sakai et al., 1998 ). The
cerebellar posterior lobe activation in the present study may reflect
the retention of a series of time intervals for 1:2.5:3.5 rhythm. The
posterior lobe activation was absent for 1:2:4 rhythm, perhaps because
the time intervals of this rhythm were metrically related and encoding
of individual time intervals was not necessary.
Right versus left hemispheric predominance
We found that metrical representation for 1:2:4 or 1:2:3 rhythms
was predominantly associated with left hemispheric activation, whereas
the nonmetrical representation for 1:2.5:3.5 rhythm was associated with
right hemispheric activation. Previous clinical studies have shown that
rhythm deficits were found after left hemispheric lesions, especially
when the left premotor and parietal areas were damaged (Brust, 1980 ;
Mavlov, 1980 ; Polk and Kertesz, 1993 ). Considering that most of the
music, especially from western countries, was metrically related
(Palmer and Kelly, 1992 ; Palmer, 1997 ), the present finding showing
activations in the left premotor and parietal areas for metrical
rhythms is consistent with these clinical studies. In contrast, the
right hemispheric activations for rhythms related with complex ratios
are consistent with an earlier study of Roland et al. (1981) , which
showed predominant right hemispheric activations in discrimination of
two rhythm patterns related with complex ratios. The right
frontoparietal areas may be involved in memory of time intervals
(Harrington et al., 1998 ), which is necessary for the nonmetrical
rhythm representation. Thus, the present results indicate that the
processing of rhythm is not confined to one cerebral hemisphere, as
Peretz (1990) has suggested.
Although we used auditory stimuli for presenting rhythms, the temporal
lobes did not show significant activation; only a small portion on the
right side was active for 1:2.5:3.5 rhythm. The frontoparietal network
active in the present study would, thus, reflect the supramodal
mechanism for rhythm processing, as suggested by Mavlov (1980) . Indeed,
it was shown that the ability in rhythm processing was preserved, even
after the lesions in the temporal lobe (Peretz and Kolinsky, 1993 ;
Peretz, 1996 ).
To summarize, we have shown that there are two modes of neural
representation for rhythm. Their selection depends on the interval ratios of the rhythm or, more precisely, on the strategy used for
encoding the rhythm, metrical or nonmetrical. Nonmetrical strategy may
require explicit processing for the individual time intervals, whereas
metrical strategy may operate automatically, and possibly implicitly,
to allow hierarchical encoding of the whole rhythm. In this regard, the
right and left hemispheric dissociation observed in the nonmetrical and
metrical rhythm processing may be closely related to the finding of
Hazeltine et al. (1997) , who showed a similar hemispheric dissociation
between explicit and implicit motor sequence learning.
 |
FOOTNOTES |
Received May 3, 1999; revised Aug. 26, 1999; accepted Sept. 3, 1999.
This study was supported by Japan Society for the Promotion of Science
(JSPS) Research for the Future program and Basic Research System
Core. K.S. was supported by JSPS Research Fellowship for Young
Scientists. We are grateful to Hiroshi Imamizu and Mitsuo Kawato at
Japan Science and Technology Corporation for their cooperation with SPM
analysis. We are also grateful to Haruo Uesugi at Department of
Neurology, University of Tokyo, who is a professional musician, for his
helpful advice on musical theory.
Correspondence should be addressed to Katsuyuki Sakai, Department of
Physiology, Juntendo University, School of Medicine, 2-1-1 Hongo,
Bunkyo-ku, Tokyo 113, Japan. E-mail: katz{at}med.juntendo.ac.jp.
 |
REFERENCES |
-
Allen G,
Buxton RB,
Wong EC,
Courchesne E
(1997)
Attentional activation of the cerebellum independent of motor involvement.
Science
275:1940-1943[Abstract/Free Full Text].
-
Brust J
(1980)
Music and language: musical alexia and agraphia.
Brain
103:367-392[Free Full Text].
-
Buckner RL,
Bandettini PA,
O'Craven KM,
Savoy RL,
Petersen SE,
Raichle ME,
Rosen BR
(1996)
Detection of cortical activation during averaged single trials of a cognitive task using functional magnetic resonance imaging.
Proc Nat Acad Sci USA
93:14878-14883[Abstract/Free Full Text].
-
Cohen JD,
Perlstein WM,
Braver TS,
Nystrom LE,
Noll DC,
Jonides J,
Smith EE
(1997)
Temporal dynamics of brain activation during a working memory task.
Nature
386:604-608[Medline].
-
Courtney SM,
Ungerleider LG,
Keil K,
Haxby JV
(1997)
Transient and sustained activity in a distributed neural system for human working memory.
Nature
386:608-611[Medline].
-
Courtney SM,
Petit L,
Maisog JM,
Ungerleider LG,
Haxby JV
(1998)
An area specialized for spatial working memory in human frontal cortex.
Science
279:1347-1351[Abstract/Free Full Text].
-
Desmond JE,
Gabrieli JDE,
Wagner AD,
Ginier BL,
Glover GH
(1997)
Lobular patterns of cerebellar activation in verbal working-memory and finger-tapping tasks as revealed by functional MRI.
J Neurosci
17:9675-9685[Abstract/Free Full Text].
-
Edmister WB,
Talavage TM,
Ledden PJ,
Weisskoff RM
(1999)
Improved auditory cortex imaging using clustered volume acquisitions.
Hum Brain Mapp
7:89-97.[Web of Science][Medline]
-
Essens PJ
(1986)
Hierarchical organization of temporal patterns.
Percept Psychophys
40:69-73[Web of Science][Medline].
-
Essens PJ,
Povel DJ
(1985)
Metrical and nonmetrical representations of temporal patterns.
Percept Psychophys
37:1-7[Web of Science][Medline].
-
Fletcher PC,
Shallice T,
Frith CD,
Frackowiak RSJ,
Dolan RJ
(1998)
The functional roles of prefrontal cortex in episodic memory. II. Retrieval.
Brain
121:1249-1256[Abstract/Free Full Text].
-
Friston KJ,
Holmes AP,
Worsley KJ,
Poline J-B,
Frith CD,
Frackowiak RS
(1995)
Statistical parametric maps in functional imaging: a general linear approach.
Hum Brain Mapp
2:189-210.
-
Fulop AC,
Kirby RH,
Coates GD
(1992)
Use of rhythm in acquisition of a computer-generated tracking task.
Percept Mot Skills
75:59-66[Web of Science][Medline].
-
Funahashi S,
Bruce CJ,
Goldman-Rakic PS
(1989)
Mnemonic coding of visual space in the monkey's dorsolateral prefrontal cortex.
J Neurophysiol
61:331-349[Abstract/Free Full Text].
-
Goldman-Rakic PS
(1996)
Regional and cellular fractionation of working memory.
Proc Natl Acad Sci USA
93:13473-13480[Abstract/Free Full Text].
-
Gordon HW,
Bogen JE
(1974)
Hemispheric lateralization of singing after intracarotid sodium amylobarbitone.
J Neurol Neurosurg Psychiatry
37:727-738[Abstract/Free Full Text].
-
Hall DA,
Haggard MP,
Akeroyd MA,
Palmer AR,
Summerfield AQ,
Elliot MR,
Gurney EM,
Bowtell RW
(1999)
"Sparse" temporal sampling in auditory fMRI.
Hum Brain Mapp
7:213-223.[Web of Science][Medline]
-
Harrington DL,
Haaland KY,
Knight R
(1998)
Cortical networks underlying mechanisms of time perception.
J Neurosci
18:1085-1095[Abstract/Free Full Text].
-
Hazeltine E,
Grafton ST,
Ivry R
(1997)
Attention and stimulus characteristics determine the locus of motor-sequence encoding A PET study.
Brain
120:123-140[Abstract/Free Full Text].
-
Ivry R
(1993)
Cerebellar involvement in the explicit representation of temporal information.
Ann NY Acad Sci
682:214-230[Web of Science][Medline].
-
Ivry RI,
Keele SW,
Diener HC
(1988)
Dissociation of the lateral and medial cerebellum in movement timing and movement execution.
Exp Brain Res
73:167-180[Web of Science][Medline].
-
Jueptner M,
Flerich L,
Weiller C,
Mueller SP,
Diener H-C
(1996)
The human cerebellum and temporal information processing-results from a PET experiment.
NeuroReport
7:2761-2765[Web of Science][Medline].
-
Kwong KK,
Belliveau JW,
Chesler DA,
Goldberg IE,
Weisskoff RM,
Poncelet BP,
Kennedy DN,
Hoppel BE,
Cohen MS,
Turner R,
Cheng H-M,
Brady TJ,
Rosen BR
(1992)
Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation.
Proc Natl Acad Sci USA
89:5675-5679[Abstract/Free Full Text].
-
Mangels JA,
Ivry RB,
Shimizu N
(1998)
Dissociable contributions of the prefrontal and neocerebellar cortex to time perception.
Cognit Brain Res
7:15-39[Medline].
-
Mavlov L
(1980)
Amusia due to rhythm agnosia in a musician with left hemisphere damage: a non-auditory supramodal defect.
Cortex
16:331-338[Web of Science][Medline].
-
Niki H,
Watanabe M
(1979)
Prefrontal and cingulate unit activity during timing behavior in the monkey.
Brain Res
171:213-224[Web of Science][Medline].
-
Nitschke MF,
Kleinschmidt A,
Wessel K,
Frahm J
(1996)
Somatotopic motor representation in the human anterior cerebellum. A high-resolution functional MRI study.
Brain
119:1023-1029[Abstract/Free Full Text].
-
Palmer C
(1997)
Music performance.
Annu Rev Psychol
48:115-138[Web of Science][Medline].
-
Palmer C,
Kelly MH
(1992)
Linguistic prosody and musical meter in song.
J Mem Lang
31:525-542.
-
Peretz I
(1990)
Processing of local and global musical information in unilateral brain damaged patients.
Brain
13:1185-1205.
-
Peretz I
(1996)
Can we lose memory for music? A case of music agnosia in a non-musician.
J Cognit Neurosci
8:481-496.
-
Peretz I,
Kolinsky R
(1993)
Boundaries of separability between melody and rhythm in music discrimination: a neuropsychological perspective.
Q J Exp Psychol
46A:301-325.
-
Peretz I,
Morais J
(1980)
Modes of processing melodies and ear asymmetry in non-musicians.
Neuropsychologia
18:477-489[Web of Science][Medline].
-
Petrides M
(1994)
Frontal lobes and behavior.
Curr Opin Neurobiol
4:207-211[Medline].
-
Polk M,
Kertesz A
(1993)
Music and language in degenerative disease of the brain.
Brain Cognit
22:98-117[Web of Science][Medline].
-
Porro CA,
Francescato MP,
Cettolo V,
Diamond ME,
Baraldi P,
Zuiani C,
Bazzocchi M,
Di Prampero PE
(1996)
Primary motor and sensory cortex activation during motor performance and motor imagery: a functional magnetic resonance imaging study.
J Neurosci
16:7688-7698[Abstract/Free Full Text].
-
Povel DJ
(1984)
A theoretical framework for rhythm perception.
Psychol Res
45:315-337[Web of Science][Medline].
-
Povel DJ,
Essens P
(1985)
Perception of temporal patterns.
Music Percept
2:411-440.
-
Robinson G,
Solomon DJ
(1974)
Rhythm is processed by the speech hemisphere.
J Exp Psychol
102:508-511[Web of Science][Medline].
-
Roland PE,
Larsen B,
Lassen NA,
Skinhøj E
(1980)
Supplementary motor area and other cortical areas in organization of voluntary movements in man.
J Neurophysiol
43:118-136[Abstract/Free Full Text].
-
Roland PE,
Skinhøj E,
Lassen NA
(1981)
Focal activation of human cerebral cortex during auditory discrimination.
J Neurophysiol
45:1139-1151[Free Full Text].
-
Sakai K,
Takino R,
Hikosaka O,
Miyauchi S,
Sasaki Y,
Pütz B,
Fujimaki N
(1998)
Separate cerebellar areas for motor control.
NeuroReport
9:2359-2363[Web of Science][Medline].
-
Stephan KM,
Fink GR,
Passingham RE,
Silbersweig D,
Ceballos-Baumann AO,
Frith CD,
Frackowiak RSJ
(1995)
Functional anatomy of the mental representation of upper extremity movements in healthy subjects.
J Neurophysiol
73:373-386[Abstract/Free Full Text].
-
Talairach J,
Tournoux P
(1988)
In: Co-planar stereotaxic atlas of the human brain. New York: Thieme.
-
Talavage TM,
Edmister WB,
Ledden PJ,
Weisskoff RM
(1999)
Quantitative assessment of auditory cortex responses induced by imager acoustic noise.
Hum Brain Mapp
7:79-88.[Web of Science][Medline]
-
Zatorre RJ,
Evans AC,
Meyer E,
Gjedde A
(1992)
Lateralization of phonetic and pitch discrimination in speech processing.
Science
256:846-849[Abstract/Free Full Text].
-
Zatorre RJ,
Evans AC,
Meyer E
(1994)
Neural mechanisms underlying melodic perception and memory for pitch.
J Neurosci
14:1908-1919[Abstract].
Copyright © 1999 Society for Neuroscience 0270-6474/99/192210074-08$05.00/0
This article has been cited by other articles:

|
 |

|
 |
 
J. L. Chen, V. B. Penhune, and R. J. Zatorre
Listening to Musical Rhythms Recruits Motor Regions of the Brain
Cereb Cortex,
December 1, 2008;
18(12):
2844 - 2854.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
J. Diedrichsen, S. E. Criscimagna-Hemminger, and R. Shadmehr
Dissociating Timing and Coordination as Functions of the Cerebellum
J. Neurosci.,
June 6, 2007;
27(23):
6291 - 6301.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
L. Stewart, K. von Kriegstein, J. D. Warren, and T. D. Griffiths
Music and the brain: disorders of musical listening
Brain,
October 1, 2006;
129(10):
2533 - 2553.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
T. Wu, K. Kansaku, and M. Hallett
How Self-Initiated Memorized Movements Become Automatic: A Functional MRI Study
J Neurophysiol,
April 1, 2004;
91(4):
1690 - 1698.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
F. Ullen, H. Forssberg, and H. H. Ehrsson
Neural Networks for the Coordination of the Hands in Time
J Neurophysiol,
February 1, 2003;
89(2):
1126 - 1135.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
R. I. Schubotz and D. Y. von Cramon
Interval and Ordinal Properties of Sequences Are Associated with Distinct Premotor Areas
Cereb Cortex,
March 1, 2001;
11(3):
210 - 222.
[Abstract]
[Full Text]
[PDF]
|
 |
|

|
 |

|
 |
 
K. Sakai, O. Hikosaka, R. Takino, S. Miyauchi, M. Nielsen, and T. Tamada
What and When: Parallel and Convergent Processing in Motor Control
J. Neurosci.,
April 1, 2000;
20(7):
2691 - 2700.
[Abstract]
[Full Text]
[PDF]
|
 |
|
|